The present invention relates to a heat-resistant engineering-plastic resin composition and a heat-resistant injection molded product made with the resin composition, such as for a surface mount PCB (printed circuit board) connector featuring high soldering-heat resistance and heat-aging resistance.
Downsizing and improvement for the performance of electronic devices and parts have brought a high density parts-mounting technology for PCB.
Consequently, not only electronic parts such as semiconductors and capacitors but also peripheral electronic parts such as connectors, which are used for data input and output, have been mounted on PCB. Conventionally, electronic parts were soldered on PCB via through holes. However, these parts mounting process have been increasingly converting to so-called SMT (surface mounting technology) in recent years to realize higher parts mounting density.
If a resin product melts or deforms when it is in contact with flow solder at high temperature, it cannot be applied in practical use. Therefore, in recent years, electronic parts having resin component such as resin substrates or connectors have been increasingly required to have enhanced soldering-heat resistance to keep the original shape without melting or deforming even when they are exposed to flow solder at high temperature.
As for the PCB connectors, polyamide-based plastics such as nylon 6,6 and polyester-based plastics such as polybutyleneterephthalate (PBT) have been used as the housing materials. However, the soldering heat-resistance of these plastics have a limitation of about 240xc2x0 C. for 10 to 60 sec.
On the other hand, since the soldering-heat resistance of 260xc2x0 C. for 10 to 60 sec is required in case for a narrow-pitch type or thin-walled type surface-mounted connector, engineers have no choice but to use so-called super engineering plastics such as a liquid crystal polymer (LCP) and polyphenylenesulfide (PPS). However, these super engineering plastics are costly comparing with conventional general-purpose engineering plastics such as nylon 6,6 and PBT. As a result, the price of the connectors increases.
Even if their high cost is tolerated, super engineering plastics are following disadvantageous in the injection molding process:
(a) They require higher temperature for injection molding, and this reduces the life time of the metal mold;
(b) The weld-line strength is low; and
(c) The molded product may have anisotropy in mechanical strength.
Concerning with solder, the tin-lead alloy has been used conventionally for flow or re-flow soldering process. However, worldwide interest on environmental problems in recent years has compelled the intensified study on lead-free solder. As a result, the practical use of lead-free solders has been steadily increasing. However, lead-free solders have higher melting point of about 20xc2x0 C. or more than conventional tin-lead alloy solder. Therefore, at least 20xc2x0 C. of increase for soldering temperature cannot be avoided in case for the lead-free solder, and at least 260xc2x0 C. for 10 to 60 sec of soldering-heat resistance has been required for the housing materials for electronic parts such as PCB connectors.
As mentioned above, conventional common engineering plastics, such as nylon 6,6 and PBT, have a limitation of soldering-heat resistance of 240xc2x0 C. for 10 to 60 sec. They do not satisfy the requirement for the soldering-heat resistance of 260xc2x0 C. for 10 to 60 sec. On the other hand, super engineering plastics such as LCP and PPS have the above-described problems of the cost increase and the disadvantages in the injection molding process.
One of the methods to solve these problems is the cross-linking of nylon 6 or PBT using ionizing radiation. However, even when nylon 6 and PBT are irradiated with electron beam or xcex3 ray, if the dose is low, sufficient cross-linking density cannot be obtained. In other words, low-dose irradiation does not satisfy the soldering-heat resistance of 260xc2x0 C. specification. On the other hand, high-dose irradiation for increasing the cross-linking density causes partial decomposition of nylon 6 and PBT during the irradiation process to deteriorate the mechanical strength of the material after heat aging test.
An aim of the present invention is to offer the low cost heat-resistant engineering-plastic composition and injection molded electronic parts such as PCB connectors which satisfies the soldering-heat resistance of 260xc2x0 C. for 10 to 60 sec, and has no problems in the injection molding process, and has excellent in heat-aging resistance. By an intensive study on the foregoing problems, the present inventors found that the intended molded product can be obtained by the following process: (a) melt-kneading (a1) an engineering plastic either having or introduced an active site for reacting with a specific functional group and (a2) either an organic compound that has both the said specific functional group and a polymerizing functional group in the same molecule or polyolefin that has the functional group described in (a1) to obtain a engineering-plastic based resin composition, (b) melt-molding of resin composition of (a), and (c) irradiating the melt-molded plastic composition with ionizing radiation. Thus, the present inventors completed the present invention.
A molded product made with a heat-resistant engineering-plastic based resin composition of the present invention can be embodied by the following methods:
{circle around (1)} (a) melt-kneading of (a1) an acid anhydride group introduced styrene based polymer and (a2) an organic compound that has in the same molecule both (a2a) a polymerizing functional group selected from the groups consisting of vinyl group, allyl group, acrylic group, and methacrylic group and (a2b) a functional group selected from the groups consisting of amino group and epoxy group;
(b) molding a resin composition of (a) into a specified shape by a melt-molding method such as an injection molding method; and
(c) cross-linking of the molded parts of (b) by ionizing radiation.
{circle around (2)} (a) melt-kneading of (a1) an oxazoline group introduced styrene based polymer and (a2) an organic compound that has in the same molecule both (a2a) polymerizing functional groups selected from the groups consisting of a vinyl group, allyl group, acrylic group, and methacrylic group and (a2b) functional group selected from the groups consisting of amino group, carboxylic acid group, hydroxyl group, epoxy group, and thiol group;
(b) molding a resin composition of (a) into a specified shape by melt-molding method such as injection molding; and
(c) cross-linking of the molded parts of (b) by ionizing radiation.
{circle around (3)} (a) melt-kneading (a1) a carboxylic acid group introduced styrene based polymer and (a2) an organic compound that has in the same molecule both (a2a) a polymerizing functional group selected from the groups consisting of vinyl group, allyl group, acrylic group, and methacrylic group and (a2b) a functional group selected from the groups consisting of amino group, hydroxyl group, epoxy group, and thiol group;
(b) molding a resin composition of (a) into a specified shape by a melt-molding method such as an injection molding; and
(c) cross-linking of the molded parts of (b) by ionizing radiation.
{circle around (4)} (a) melt-kneading (a1) an acid anhydride group introduced polyphenylene ether and (a2) an organic compound that has in the same molecule both (a2a) a polymerizing functional group selected from the groups consisting of vinyl group, allyl group, acrylic group, and methacrylic group and (a2b) a functional group selected from the groups consisting of amino group and epoxy group;
(b) molding a resin composition of (a) into a specified shape by a melt-molding method such as an injection molding; and
(c) cross-linking of the molded parts of (b) by ionizing radiation.
{circle around (5)} (a) melt-kneading (a1) polybutyleneterephthalate and (a2) an organic compound that has in the same molecule both (a2a) a polymerizing functional group selected from the groups consisting of vinyl group, allyl group, acrylic group, and methacrylic group and (a2b) a functional group selected from the groups consisting of amino group, hydroxyl group, epoxy group, and carboxylic acid group;
(b) molding a resin composition of (a) into a specified shape by a melt-molding method such as an injection molding; and
(c) cross-linking of the molded parts of (b) by ionizing radiation.
{circle around (6)} (a) melt-kneading (a1) polyamide resin, such as nylon 6, nylon 6,6, nylon 6,12, or nylon 6T, and (a2) an organic compound that has in the same molecule both (a2a) a polymerizing functional group selected from the groups consisting of vinyl group, allyl group, acrylic group, and methacrylic group and (a2b) an atomic group having a functional group selected from the groups consisting of epoxy group, carboxylic acid group, and acid anhydride group;
(b) molding a resin composition of (a) into a specified shape by a melt-molding method such as an injection molding; and
(c) cross-linking of the molded parts of (b) by ionizing radiation.
{circle around (7)} (a) melt-kneading (a1) polybutyleneterephthalate and (a2) a polyolefin having a graft-polymerized or copolymerized monomer that react with polyester;
(b) molding a resin composition of (a) into a specified shape by a melt-molding method such as an injection molding; and
(c) cross-linking of the molded parts of (b) by ionizing radiation.
{circle around (8)} (a) melt-kneading (a1) polyamide resin, such as nylon 6, nylon 6,6, nylon 6,12, or nylon 6T, and (a2) polyolefin having a graft-polymerized or copolymerized monomer that reacts with polyamide;
(b) molding a resin composition of (a) into a specified shape by a melt-molding method such as an injection molding method; and
(c) cross-linking of the molded parts of (b) by ionizing radiation.
{circle around (9)} (a) melt-kneading (a1) an acid anhydride group introduced polyphenylene ether and (a2) a polyolefin having a graft-polymerized or copolymerized monomer that reacts with an acid anhydride group of the polyphenylene ether;
(b) molding a resin composition of (a) into a specified shape by a melt-molding method such as an injection molding method; and
(c) cross-linking of the molded parts of (b) by ionizing radiation.
Specific examples of item {circle around (1)} are an acid anhydride introduced styrene based polymer include a copolymer of maleic anhydride and styrene and a copolymer of maleic anhydride, styrene, and acrylonitrile. These polymers can be obtained, for example, by radical copolymerization of monomers such as styrene, acrylonitrile, and maleic anhydride. The desirable content of maleic anhydride in the above-mentioned copolymer in a range of 0.1 to 10 mol %, more desirably 0.5 to 5 mol %. If the content is less than 0.1 mol %, a sufficient cross-linking degree to satisfy the required soldering-heat resistance may not be obtained. On the other hand, even if the copolymerization exceeding 10 mol % is carried out, a better result cannot be obtained. Moreover, the flexural modulus and mechanical strength may decrease, and the material price may increase. As for the organic compound that has in the same molecule both (a) a polymerizing functional group selected from the groups consisting of vinyl group, allyl group, acrylic group, and methacrylic group and (b) an atomic group having a functional group selected from the groups consisting of amino group, epoxy group, and hydroxyl group, the following examples can be shown: aminoethylvinyl ether, 4-aminostyrene, 4-hydroxystyrene, allyl phenol, allyl glycidyl ether, allylamine, diallylamine, glycidylacrylate, glycidylmethacrylate, and aminoethylmethacrylate. In these examples, it is desirable to use a compound that has a methacrylic group and an epoxy group in the same molecule, such as glycidylmethacrylate, because it has a better quality in melt-mixing with the foregoing polymers. The desirable amount for the organic compound is in a range of 0.5 to 20 parts by weight per 100 parts by weight of the acid anhydride group introduced styrene based polymer, more desirably 1 to 10 parts by weight. If less than 0.5 parts by weight, the cross-linking degree may be insufficient to meet the required soldering-heat resistance. On the other hand, even if the added amount exceeds 20 parts by weight, a better result cannot be obtained. Moreover, the processibility of melt-mixing and injection molding may decrease.
Specific examples of oxazoline group introduced styrene based polymers for item {circle around (2)} include a copolymer of styrene and 2-propenyl oxazoline and a copolymer of styrene, acrylonitrile, and 2-propenyl oxazoline. These polymers can be synthesized, for example, by radical copolymerization of monomers such as styrene, acrylonitrile, and 2-propenyl oxazoline. It is desirable that the 2-propenyl oxazoline content in the above-mentioned copolymers is in a range of 0.1 to 10 mol %, more desirably 0.5 to 5 mol %. If the copolymerization ratio is less than 0.1 mol %, a sufficient cross-linking degree to meet the required soldering-heat resistance may not be obtained. On the other hand, even if the copolymerization exceeding 10 mol % is carried out, a better result cannot be obtained. Moreover, the flexural modulus and mechanical strength may decrease, and the material price may increase.
As for the organic compound that has in the same molecule both (a) a polymerizing functional group selected from the groups consisting of vinyl group, allyl group, acrylic group, and methacrylic group and (b) an atomic group having a functional group selected from the groups consisting of hydroxyl group, carboxylic acid group, and thiol group, the following examples can be shown: 4-hydroxystyrene, 4-aminostyrene, allyl phenol, acrylic acid, glycidylacrylate, 2-acryloyloxyethylsuccinate, 2-acryloyloxyethyl phthalate, methacrylic acid, 2-methacryloyloxyethylsuccinate, and 2-methacryloyloxyethyl phthalate.
In these examples, it is desirable to use a compound that has a methacrylic group and a carboxylic acid group in the same molecule, such as methacrylic acid and 2-methacryloyloxyethylphthalate. The desirable added amount of organic compound is in a range of 0.1 to 20 parts by weight per 100 parts by weight of the oxazoline group containing styrene based polymer, and more desirably 0.5 to 10 parts by weight. If less than 0.1 part by weight, the cross-linking degree may be insufficient to meet the required soldering-heat resistance. On the other hand, even if the added amount exceeds 20 weight parts, a better result cannot be obtained. Moreover, the processibility of melt-mixing and injection molding may decrease.
Specific examples of carboxyl acid group introduced styrene based polymer of item {circle around (3)} include a copolymer of styrene and methacrylic acid; a copolymer of styrene, acrylonitrile, and methacrylic acid; a copolymer of styrene, acrylonitrile, and acrylic acid; a copolymer of styrene and itaconic acid; and other plastics based on carboxylic acid-modified polystyrene. These polymers can be synthesized by radical polymerization and other known methods.
The content of the carboxylic acid group in the above styrene-based copolymer can be controlled by changing the ratio of the copolymerization ratio of the unsaturated carboxylic acid monomer. The desirable content of unsaturated carboxylic acid monomer is 1 to 20 weight %, more desirably 2 to 10 weight %. If less than 1 weight %, the soldering-heat resistance may not be sufficient. If more than 20 weight %, deterioration of processibility for injection molding, and impact resistance may occur, and other unexpected problems may arise.
As for the compound that has a carbon-carbon unsaturated bond and amino group, a hydroxyl group, epoxy group, and thiol group, in the same molecule, the following examples can be shown: allylamine, diallylamine, 4-aminostyrene, 2-hydroxyethylacrylate, 2-hydroxyethylmethacrylate, allyl alcohol, ethyleneglycol monomethacrylate, diethyleneglycol monomethacrylate, trimethylolpropane monomethacrylate, trimethylolpropane dimethacrylate, p-hydroxystyrene, m-hydroxystyrene, and ethyl-xcex1-hydroxymethyl methacrylate, glycidylmethacrylate, 4-mercaptostyrene.
As for the ratio of (a) the styrene-based copolymer having a carboxyl acid group to (b), the compound that has a carbon-carbon unsaturated bond and amino group, hydroxyl group, epoxy group, and thiol group in the same molecule, the desirable ratio of compound (b) is in a range of 1 to 30 parts by weight per 100 parts by weight of styrene based copolymer (a), when the content of the carboxyl acid group in the styrene-based polymer (a) is 1 to 20 weight %. If less than 1 part by weight, the soldering-heat resistance may not be sufficient. If more than 30 weight parts, the processibility for molding may decrease and the price may become undesirable.
Item {circle around (4)} specifies polyphenylene ether having an acid anhydride group. The polymer can be synthesized by the known method of chemically modification for the molecular terminal of the polyphenylene ether to introduce an acid anhydride group such as maleic anhydride.
As for the organic compound that has in the same molecule both (a) a polymerizing functional group selected from the groups consisting of vinyl group, allyl group, acrylic group, and methacrylic group and (b) a functional group selected from the groups consisting of amino group, epoxy group, and hydroxyl group, the following examples can be shown: aminoethyl vinyl ether, 4-aminostyrene, 4-hydroxystyrene, allylamine, diallylamine, glycidylacrylate, glycidylmethacrylate, and aminoethylmethacrylate. In these examples, it is desirable to use a compound that has a methacrylic group and an epoxy group in the same molecule, such as glycidylmethacrylate, because it has better processibility of melt-mixing. The desirable amount of organic compound is in a range of 0.1 to 20 parts by weight per 100 parts by weight of the polyphenylene ether having an acid anhydride group, more desirably 0.5 to 10 parts by weight. If less than 0.1 parts by weight, the cross-linking degree may be insufficient to meet the required soldering-heat resistance. Even if the added amount exceeds 20 parts by weight, a better result cannot be obtained. Moreover, the processibility of melt-mixing and injection molding may be decrease.
Item {circle around (5)} specifies polybutyleneterephthalate. As for the organic compound that is to be added to the polybutyleneterephthalate and that has in the same molecule both (a) a polymerizing functional group selected from the groups consisting of vinyl group, allyl group, acrylic group, and methacrylic group and (b) a functional group selected from the groups consisting of amino group, carboxylic acid group, epoxy group, and hydroxyl group, the following examples can be shown: 4-hydroxystyrene, 4-aminostyrene, allyl phenol, acrylic acid, glycidylacrylate, methacrylic acid, glycidylmethacrylate, aminoethylmethacrylate, 2-acryloyloxyethylsuccinate, 2-acryloyloxyethyl phthalate, 2-methacryloyloxyethylsuccinate, and 2-methacryloyloxyethyl phthalate. In these examples, it is desirable to use a compound that has in the same molecule (a) a methacrylic group and (b) either a carboxylic acid group or an epoxy group, such as methacrylic acid and glycidylmethacrylate, because it has better processibility of melt-mixing with the polybutyleneterephthalate. The desirable amount of organic compound to be added is in a range of 0.1 to 20 parts by weight per 100 parts by weight of the polybutyleneterephthalate, more desirably 0.5 to 10 parts by weight. If less than 0.1 parts by weight, the cross-linking may be insufficient to meet the required soldering-heat resistance. Even if the added amount exceeds 20 parts by weight, a better result cannot be obtained. Moreover, the processibility of melt-mixing and injection molding may decrease.
Item {circle around (6)} specifies polyamide resin. As for the organic compound that is to be added to the polyamide resin, such as nylon 6, nylon 6,6, nylon 6,12, or nylon 6T, and that has in the same molecule both (a) a polymerizing functional group selected from the groups consisting of vinyl group, allyl group, acrylic group, of epoxy group and carboxylic acid group, the following examples can be it shown: acrylic acid, glycidylacrylate, methacrylic acid, glycidyl methacrylate, 2-acryloyloxyethylsuccinate, 2-acryloyloxyethyl phthalate, 2-methacryloyloxyethyl succinate, and 2-methacryloyloxyethyl phthalate. In these examples, it is desirable to use a compound that has a methacrylic group and an epoxy group in the same molecule, such as glycidylmethacrylate. The desirable amount of organic compound to be added is in a range of 0.1 to 20 parts by weight per 100 parts by weight of the polyamide resin, more desirably 0.5 to 10 parts by weight. If less than 0.1 parts by weight, the cross-linking degree may be insufficient to meet the required soldering-heat resistance. Even if the added amount exceeds 20 parts by weight, a better result cannot be obtained. Moreover, the processibility of melt-mixing may decrease.
As for the monomers which reacts with polyesters for item {circle around (7)}, it can be shown that monomers which contains carboxyl acid group, acid anhydride group, epoxy group, oxazoline group, carbodiimide group, isocyanate group, hydroxyl group, silanol group, etc. In particular, it is desirable to use the monomers such as maleic anhydride, glycidylmethacrylate, acrylic acid, methacrylic acid and so on.
Item {circle around (8)} specifies a monomer that reacts with polyamide. As for the orgamic compound to be added to polyamide, the monomers containing carboxylic acid group, acid anhydride group, epoxy group, oxazoline group, carbodiimide group, isocyanate group, hydroxyl group, silanol group, etc can be shown as examples. In particular, it is desirable to use the monomers of maleic anhydride, glycidylmethacrylate, acrylic acid, methacrylic acid, etc.
Item {circle around (9)} specifies a monomer that reacts with an acid anhydride group of polyphenylene ether. As for the organic compound to be added to the acid anhydride group modified polyphenylene ether, the monomers containing amino group and epoxy group are exemplified as desirable ones.
The foregoing monomers may be graft-polymerized or copolymerized with general-purpose polyolefin, without any specific limitations, such as polyethylene, ethylene-vinyl acetate copolymer (EVA), ethylene-ethylacrylate copolymer (EEA), ethylene-octene copolymer, ethylene-propylene copolymer, ethylenebutene copolymer, ethylene-hexene copolymer, or ethylene-propylene-diene terpolymer.
Amorphous engineering plastics including polyphenylene ether, polystyrene, and styrene-acrylonitrile copolymer are generally advantageous for small shrinkage in injection molding process, and their molded products have small warp and small anisotropy in mechanical properties. However, they have some disadvantages such as stress-cracking in solvents. On the other hand, crystalline engineering plastics including polybutyleneterephthalate and polyamide are advantageous in that they are excellent in solvent resistance and stress-cracking and are suitable for thin wall injection molding. They are, however, disadvantageous in that they have large molding shrinkage and the molded products apt to warp.
In order to obtain a balance between the processibility in injection molding and the physical properties, researchers and engineers have conducted intensive studies on polymer alloys of amorphous engineering plastics and crystalline engineering plastics. Typical examples of these polymer alloys include a polymer alloy of polyphenylene ether and polybutyleneterephthalate and a polymer alloy of polyphenylene ether and polyamide, which are already in practical use.
However, these engineering plastic-based alloys are not sufficient in heat resistance. None of them satisfies a soldering-heat resistance test even at 240xc2x0 C. specification. Therefore, they cannot be used to the applications that require a soldering-heat resistance of a 260xc2x0 C. specification.
The present invention is effective for improvement of the soldering heat-resistance of these polymer alloys as well. More specifically, all of the following combinations can be used to obtain heat-resistant polymer alloys: a polyphenylene ether-based resin composition of Item {circle around (4)} and a polybutyleneterephthalate based resin composition of Item {circle around (5)}, a polyphenylene ether based resin composition of Item {circle around (4)} and a polyamide based resin composition of Item {circle around (6)}, a polyphenylene ether based resin composition of Item {circle around (9)} and a polybutyleneterephthalate based resin composition of Item {circle around (7)}, and a polyphenylene ether based resin composition of Item {circle around (9)} and a polyamide based resin composition of Item {circle around (8)}. Polymer alloys combine good processibility in injection molding and physical properties, such as stress-cracking and solvent resistance. In addition, they can be cross-linked by ionizing radiation to obtain molded products that can satisfy the soldering-heat resistance of a 260xc2x0 C. specification.
The above-described composites of the present invention can be further combined with multifunctional monomers to obtain plastic compositions that have further enhanced soldering heat resistance and heat aging property. More specifically, they satisfy a soldering-heat resistance of 280xc2x0 C. specification and heat aging test of 140xc2x0 C. for seven days. If necessary, known chemicals, such as a coloring agent, lubricant, a stabilizer, an antioxidant, a flame retardant, and a cross-linking promoter, may be added to the compositions of the present invention.
The compositions of the present invention can be produced by using a known mixing machine, such as single screw or a twin screw extruder type of melt mixers. The materials for the compositions can be molded by using a known injection molding machine.
The molded products can be irradiated not only by xcex3-rays from cobalt 60, but also by X-rays and xcex1-rays. When accelerated electron beams are used for the irradiation, the accelerating voltage can be adjusted in accordance with the thickness of the molded product.